Tacrolimus (also referred to as FK-506) is a compound known to have immunosuppressive activity. As an immunosuppressive, it is used in a variety of situations such as organ transplantations and eczema treatment. The structure of tacrolimus includes a macrocyclic lactone, and various structurally related macrolide compounds are known.
Relevant art: US 2006/0035918; U.S. Pat. No. 5,457,111.